feat: add trending/leaderboard for collections

New collection_favorites table lets users star public collections.
/collections/explore mirrors the recipe explore page: trending (star
count in last 7 days) and recently-added public collections. Linked
from the "Discover" button on the collections page.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/components/collections/collections-page-content.tsx

@@ -1,9 +1,11 @@
 "use client";
 import { useTranslations } from "next-intl";
 import Link from "next/link";
-import { FolderOpen } from "lucide-react";
+import { FolderOpen, Flame } from "lucide-react";
 import { Badge } from "@/components/ui/badge";
+import { buttonVariants } from "@/components/ui/button";
 import { NewCollectionButton } from "@/components/social/new-collection-button";
+import { cn } from "@/lib/utils";
 
 type Collection = {
   id: string;
@@ -27,7 +29,13 @@ export function CollectionsPageContent({ collections }: Props) {
           <h1 className="text-3xl font-bold tracking-tight">{t("title")}</h1>
           <p className="text-muted-foreground mt-1">{t("subtitle")}</p>
         </div>
-        <NewCollectionButton />
+        <div className="flex items-center gap-2">
+          <Link href="/collections/explore" className={cn(buttonVariants({ variant: "outline", size: "sm" }), "gap-1.5")}>
+            <Flame className="h-4 w-4 text-orange-500" />
+            {t("discoverTitle")}
+          </Link>
+          <NewCollectionButton />
+        </div>
       </div>
 
       {collections.length === 0 ? (